In order to better understand the cellular mechanisms involved in the diverse effects of the environmental contaminant, dioxin, we will study specific receptor binding factors (RBFs) for the Ah receptor in chromatin. The differential sensitivity of various animal species and tissues to dioxin may be explained, in part, by the absence or presence of certain AhRBFs in the nuclear matrix. In addition, the antiestrogenic actions of dioxin may be explained by interaction of the Ah receptor with certain uterine estrogen RBFs. These studies will also address the poor correlation between biological effectiveness of some compounds and their in vitro binding affinity for the Ah receptor or for receptor complex binding to dioxin response elements. We must first purify select liver and uterine AhRBFs. Determination of their amino acid sequences will allow for comparisons with other DNA binding proteins, especially RBFs for steroid hormones. Preparation of antibodies to these AhRBFs will allow us to determine if these chromosomal proteins are associated with the nuclear matrix in a species and tissue specific manner. Studies are also proposed to investigate the role of AhRBFs in gene transcription utilizing both transient and stable transfection experiments. We will determine if and where AhRBFs are associated with known dioxin-inducible genes, such as CYP1A1 or CYP1A2 and also determine the consensus DNA sequence to which these AhRBFs bind.